Winch systems consisting of two drums, a geared rotary actuator, an electric motor and an overtravel stop device are known. In such systems, a unidirectional rotational load is applied to the winch output through cables which are attached to the drums to which a force is applied such as that when a load is being lifted by the winch. It is required that the system will be irreversible in the direction of the applied load. Even though an included gear train is of a self-locking type, irreversibility in a vibration environment is not reliably provided.